Ecophysiology of the Oral Opportunistic Pathogen Actinobacillus actinomycetemcomitans with Special Emphasis on Leukotoxin Production

抄録

Actinobacillus actinomycetemcomitans, a Gram-negative periodontopathic bacterium, produces a leukotoxin belonging to the RTX family. The leukotoxin determinant consists of four contiguous genes designated ltxC, ltxA, ltxB and ltxD. Although the ltx operon appears to be present in all A. actinomycetemcomitans strains, the level of toxin expression varies considerably between the strains. Several molecular genetic studies have indicated that the difference in leukotoxin production among strains was dependent on the structure of the leukotoxin promoter region. In addition, chemostat culture studies revealed that the production of leukotoxin was influenced greatly by various environmental factors, e.g. growth rate, oxygen, bicarbonate, external sugar level, and pH. In this paper, the state of knowledge of leukotoxin expression in A. actinomycetemcomitans is reviewed.